Study of the fetus in vivo provides a simple mammalian system that permits investigation of early neurobehavioral development. Understanding the prenatal roots of behavioral organization is fundamental to a deeper understanding of the adaptive capacities and needs of fetuses, full-term neonates, and preterm infants (which are, in essence, fetuses asked to adapt to an age atypical environment). Behavioral organization, which refers to the nonrandom distribution of motor behavior in space and time, is evident both during spontaneous motor activity and during responses to sensory stimulation. Organization can be objectively characterized and quantified in the synchronous movement of different body regions, temporal patterns in motor activity, interlimb or intersegmental coordination, and spatiotemporal sets in which spatial and temporal movement variables alternate between two or more stable states. The control parameters that generate an organized pattern of fetal movement constitute an action system. Patterns of movement expressed by an action system may be prescribed by elements of the nervous system, or may emerge as a product of variable motor production, selection of motor synergies, contextual constraint, and self-organization. This proposal will investigate processes of variation, selection, context, and self-organization in the prenatal development of action systems in the rat fetus. Four specific aims are addressed. (1) Spatiotemporal organization of fetal motor activity and developmental changes in basic patterns of motor coordination will be characterized by kinematic analysis of spontaneous fetal behavior and quantitative analysis of movement time- series. (2) Organization of fetal action patterns will be examined through kinematic analysis of motor patterns evoked by sensory stimulation and perturbed by sensory or biomechanical manipulations. These experiments will evaluate the hypothesis that coordinated action in the fetus is not expressed immediately in response to stimulation, but emerges as a process of selection from more generalized motor activity. (3) The capacity of the fetus to exhibit motor learning will be assessed in a paradigm that uses biomechanical manipulations to facilitate the temporal and spatial coupling of movements in different limbs. These studies will chart the development of functional kinesthetic senses in the fetus, and will assess the ability of the fetus to acquire and express new motor patterns in utero. (4) The relevance of prenatal motility, if any, for the postnatal development of behavior remains a subject of controversy and speculation. Prenatal-neonatal continuity in motor development will be addressed in experiments designed to test whether improved motor performance or novel motor patterns acquired in utero can persist across the transition of birth to influence motor behavior of the neonate.